feat: add fluxer upstream source and self-hosting documentation

- Clone of github.com/fluxerapp/fluxer (official upstream)
- SELF_HOSTING.md: full VM rebuild procedure, architecture overview,
  service reference, step-by-step setup, troubleshooting, seattle reference
- dev/.env.example: all env vars with secrets redacted and generation instructions
- dev/livekit.yaml: LiveKit config template with placeholder keys
- fluxer-seattle/: existing seattle deployment setup scripts

fluxer/fluxer_gateway/config/sys.config.template

@@ -0,0 +1,22 @@
+[
+    {kernel, [
+        {logger_level, ${LOGGER_LEVEL}},
+        {logger, [
+            {handler, default, logger_std_h, #{
+                level => ${LOGGER_LEVEL},
+                config => #{
+                    type => standard_io
+                }
+            }}
+        ]},
+        {inet_dist_use_interface, {0,0,0,0}},
+        {inet_backend, socket},
+        {inet_dist_listen_options, [{reuseaddr, true}]}
+    ]},
+    {sasl, [
+        {errlog_type, error}
+    ]},
+    {inet, [
+        {lookup, [native, file, dns]}
+    ]}
+].

fluxer/fluxer_gateway/config/vm.args.src

@@ -0,0 +1,11 @@
+${FLUXER_GATEWAY_NODE_FLAG} ${FLUXER_GATEWAY_NODE_NAME}
++K true
++A30
+-env ERL_MAX_PORTS 4096
+-env ERL_PROCESSES 262144
++P 262144
++Q 65536
++S 4:4
++zdbbl 32768
+-kernel logger_level ${LOGGER_LEVEL}
+-kernel inet_backend socket

fluxer/fluxer_gateway/config/vm.args.template

@@ -0,0 +1,11 @@
+${FLUXER_GATEWAY_NODE_FLAG} ${FLUXER_GATEWAY_NODE_NAME}
++K true
++A30
+-env ERL_MAX_PORTS 4096
+-env ERL_PROCESSES 262144
++P 262144
++Q 65536
++S 4:4
++zdbbl 32768
+-kernel logger_level ${LOGGER_LEVEL}
+-kernel inet_backend socket